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<!-- Ported from the OpenGL Samples Pack: github.com/g-truc/ogl-samples/blob/master/tests/gl-320-draw-instanced.cpp -->
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<head>
    <title>WebGL 2 Samples - draw_instanced</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
    <link rel="stylesheet" href="style.css">
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<body>
    <div id="info">WebGL 2 Samples - draw_instanced</div>
    <p id="description">
        This samples demonstrates the use of gl.DrawArraysInstanced()
    </p>

    <script id="vs" type="x-shader/x-vertex">
        #version 300 es
        #define POSITION_LOCATION 0
        #define COLOR_LOCATION 1
        
        precision highp float;
        precision highp int;

        layout(location = POSITION_LOCATION) in vec2 pos;
        layout(location = COLOR_LOCATION) in vec4 color;
        flat out vec4 v_color;

        void main()
        {
            v_color = color;
            gl_Position = vec4(pos + vec2(float(gl_InstanceID) - 0.5, 0.0), 0.0, 1.0);
        }
    </script>

    <script id="fs" type="x-shader/x-fragment">
        #version 300 es
        precision highp float;
        precision highp int;

        flat in vec4 v_color;
        out vec4 color;

        void main()
        {
            color = v_color;
        }
    </script>

    <script src="utility.js"></script>
    <script>
    (function () {
        'use strict';

        // -- Init Canvas
        var canvas = document.createElement('canvas');
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;
        document.body.appendChild(canvas);

        // -- Init WebGL Context
        var gl = canvas.getContext('webgl2', { antialias: false });
        var isWebGL2 = !!gl;
        if(!isWebGL2) {
            document.getElementById('info').innerHTML = 'WebGL 2 is not available.  See <a href="https://www.khronos.org/webgl/wiki/Getting_a_WebGL_Implementation">How to get a WebGL 2 implementation</a>';
            return;
        }

        // -- Init Program
        var program = createProgram(gl, getShaderSource('vs'), getShaderSource('fs'));
        gl.useProgram(program);

        // -- Init Vertex Array
        var vertexArray = gl.createVertexArray();
        gl.bindVertexArray(vertexArray);

        // -- Init Buffers
        var vertexPosLocation = 0;  // set with GLSL layout qualifier
        var vertices = new Float32Array([
            -0.3, -0.5,
             0.3, -0.5,
             0.0,  0.5
        ]);
        var vertexPosBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, vertexPosBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
        gl.enableVertexAttribArray(vertexPosLocation);
        gl.vertexAttribPointer(vertexPosLocation, 2, gl.FLOAT, false, 0, 0);

        var vertexColorLocation = 1;  // set with GLSL layout qualifier
        var colors = new Float32Array([
            1.0, 0.5, 0.0,
            0.0, 0.5, 1.0
        ]);
        var vertexColorBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, colors, gl.STATIC_DRAW);
        gl.enableVertexAttribArray(vertexColorLocation);
        gl.vertexAttribPointer(vertexColorLocation, 3, gl.FLOAT, false, 0, 0);
        gl.vertexAttribDivisor(vertexColorLocation, 1); // attribute used once per instance

        gl.bindVertexArray(null);

        // -- Render
        gl.clearColor(0.0, 0.0, 0.0, 1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);

        gl.bindVertexArray(vertexArray);

        gl.drawArraysInstanced(gl.TRIANGLES, 0, 3, 2);

        // -- Delete WebGL resources
        gl.deleteBuffer(vertexPosBuffer);
        gl.deleteBuffer(vertexColorBuffer);
        gl.deleteProgram(program);
        gl.deleteVertexArray(vertexArray);
    })();
    </script>
    <div id="highlightedLines"  style="display: none">#L98</div>
</body>
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